In today's radio communications networks a number of different technologies are used, such as Long Term Evolution (LTE), LTE-Advanced, Wideband Code Division Multiple Access (WCDMA), Global System for Mobile communications/Enhanced Data rate for GSM Evolution (GSM/EDGE), Worldwide Interoperability for Microwave Access (WiMax), or Ultra Mobile Broadband (UMB), just to mention a few possible implementations. A radio communications network comprises radio base stations providing radio coverage over at least one respective geographical area, the geographical area may be called a cell. The cell definition may also incorporate frequency bands used for transmissions, which means that two different cells may cover the same geographical area but using different frequency bands. User equipments (UE) are served by the respective radio base station and are communicating with respective radio base station. The user equipments transmit data over an air or radio interface to the radio base stations in uplink (UL) transmissions and the radio base stations transmit data over an air or radio interface to the user equipments in downlink (DL) transmissions.
In e.g. the LTE uplink user equipment transmit power control is applied in order to lower interference and reduce user equipment battery consumption. The power control formula for transmit or transmission power for uplink shared channel, PPUSCH,c(i) is described in Third Generation Partnership Project (3GPP) TS 36.213 Physical Layer procedures, v 10.4.0 section 5.1.1 where
            P              PUSCH        ,        c              ⁡          (      i      )        =      min    ⁢          {                                                                                    P                                      CMAX                    ,                    c                                                  ⁡                                  (                  i                  )                                            ,                                                                                          10                ⁢                                                                  ⁢                                                      log                    10                                    ⁡                                      (                                                                  M                                                  PUSCH                          ,                          c                                                                    ⁡                                              (                        i                        )                                                              )                                                              +                                                P                                      O_PUSCH                    ,                    c                                                  ⁡                                  (                  j                  )                                            +                                                                    α                    c                                    ⁡                                      (                    j                    )                                                  ·                                  PL                  c                                            +                                                Δ                                      TF                    ,                    c                                                  ⁡                                  (                  i                  )                                            +                                                f                  c                                ⁡                                  (                  i                  )                                                                        }        ⁢                         [        dBm        ]            where,PCMAX,c(i) is the configured user equipment maximum transmit power,MPUSCH,c is the bandwidth of the Physical Uplink Shared Channel (PUSCH) resource assignment expressed in number of resource blocks, this term compensates for varying assigned bandwidth,PO_PUSCH,c(j) is a configurable power target, this parameter depends on j where j is set dependent on if the transmission relates to a normal transmission, a Semi Persistent Scheduling (SPS) transmission or an Random Access Response message,αcε{0, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1} is a 3-bit parameter and relates to path-loss compensation, i.e. how much the user equipment should compensate its transmit power dependent on increasing/decreasing path-loss towards the radio base station,PLc is the downlink path loss estimate,ΔTF,c (i)=10 log10((2BPRE·Ks−1)·βoffsetPUSCH) is an offset dependent on if the transmission is a transmission only containing uplink control information or not,fc(i) is a dynamic part controlled by power control commands sent in the grant on the downlink control channel. It can either be absolute commands or accumulative commands.
The user equipment transmit power is hence controlled by the radio communications network, e.g. a radio base station, with one slow component, configuring PO_PUSCH,c(j) and αc, and one fast component in the power control commands fc(i). The different components may be used to provide a good received signal to interference and noise ratio (SINR) while keeping the interference to neighbouring cells low.
In 3GPP the potential introduction of more flexible Time Division Duplex (TDD) configurations has been assessed. In TDD the same frequency resources are used both for uplink and downlink transmissions where resources are divided between the links in time. The division is in LTE controlled by the eNodeB, i.e. the radio base station, which signals an uplink/downlink pattern to the user equipment, where the current standard supports configurations with from around 10% up to around 60% uplink. So far, the configuration is performed using system broadcast and is hence changed relatively slowly. If neighbouring cells use different TDD configurations so called eNodeB-to-eNodeB interference may occur in addition to UE-to-UE interference. eNodeB-to-eNodeB interference is the downlink transmission in one cell that will be seen as interference for a simultaneous uplink transmission, on the same frequency, in a different cell. This interference may in some deployments be many multitudes stronger than typical uplink interference stemming from other transmitting user equipments due to higher output power from a radio base station compared to a user equipment and also because of possibly different propagation conditions between radio base stations as compared to between user equipments and radio base stations. Put another way, during a 10 ms radioframe, for a given radio base station serving the user equipment, the UL subframes in which eNodeB-to-eNodeB interference occurs, due to the fact that another radio base station is using the same subframes for DL transmission, experience a higher level of interference and noise as compared to UL subframes for which there are no eNodeB-to-eNodeB interference since all radio base stations are using these subframes for UL transmissions.
In TDD systems the same frequency is used for both uplink and downlink transmissions. To protect the system from interference between uplink and downlink a guard period is inserted between uplink and downlink periods. This guard period when switching from downlink to uplink is set such that the user equipments will have time to switch from receiving to transmitting but also to be longer than the propagation delay from radio base station received with significant interfering power. In some special conditions the propagation properties may change such that transmissions of radio base stations from further away may be received with high power. In these cases the guard period may not have been set to a large enough value and high interference may then be experienced in the first uplink subframe, which first uplink subframe being the first in time UL subframe after a downlink/switching subframe.
There is also a possibility that there are multiple TDD carriers on adjacent frequencies in the same frequency band. For example, in the 2300-2400 MHz band, there may be multiple carriers, each using e.g. a 20 MHz bandwidth. Due to imperfect filtering, the different carriers cause interference to each other. For example, the downlink transmission on one carrier causes interference to the uplink reception on another carrier. At the radio base station receiver side, interference levels may then be higher during the subframes, where downlink transmission occurs on the adjacent carriers, as compared to the subframes, where also the adjacent carriers are used for uplink.
The UL/DL interference may also occur in case of Global Positioning System (GPS) sync failure in any neighbouring TDD cells. In this case, the unsynchronized radio base station may interfere with the other radio base station(s) and similar situations may occur.
There are possibilities also that Band 7, i.e. DL frequency band at 2620-2670 MHz and UL 2500-2570 MHz, Frequency Division Duplex (FDD) systems and band 38, i.e. frequency band of 2570-2620 MHz, TDD systems may experience similar problems due to adjacent channel interference. Hence, even for an FDD carrier, interference may be relatively high in certain subframes, where downlink transmissions occur on an adjacent carrier, as compared to other subframes, where no downlink but user equipment uplink transmissions occurs.
Currently, the radio base station configures the user equipment with power control parameters for the user equipment to use when determining, at the user equipment, transmit power for transmissions to the radio base station. The radio base station may then use e.g. the power command fc(i) to tune the transmit power of the user equipment. The power control parameters may be periodically updated and the power command fc(i) changes the transmit power in a rather slow manner. The types of interferences mentioned above introduce a rather drastic interference increase in some subframes, reducing the performance of the radio communications network.